I just can't imagine saying that sentence. It's not an idiomatic Japanese sentence if you're trying to use it with the meaning of "How much money do you want for something that I'm going to buy from you?" In that case I would prefer 何円 or 何ドル (if you are in the US saying that). Even then, 何円がほしいですか just doesn't sound like a natural way to ask that -- I can't explain why, and my non-native-speaker-sense may not be accurate here, but that's my feeling.

(You may be wondering why 何円 is OK but 何金 is not. The reason is that 円 is a counter, that is, you can say 一円, 二円, 三円, and so on. You cannot say 一金, ニ金 -- it's not countable. This is sort of like how in English you can say "How many boxes?" and "How many stalks of wheat?" but not "How many wheats?")